Renewing the rear preload knob's full usability

[CycleRob]

It started gradually. I kept having to add more preload to keep my bike's handling light-n-easy. When you jack up the rear preload on any M/C, the ease of the bike to "fall into" a corner gets better. There is a maximum that should be avoided, because stability suffers, but with most every bike, that setting is not attainable with normal adjustments.

My problem was that the maximum setting no longer did the job. Loosening the rear shock's preload knob to the minimum stop gave me my answer. There were about 4 turns of freewheeling nothingness before the minimum stop setting. I saw no oily dirt evidence of any leaks or weeps. Apparently the constant high pressure on the shock's preload piston and other junctions weeps preload fluid over time so slowly it evaporates.

My original stock BMW shock had the same disfunction. Filling it the usual way thru the adjuster body's banjo bolt hole helps a lot but doesn't give 100% utilization. I did the same shadetree mod on my sagging stock BMW shock as will be shown performed on my sagging Ohlins rear shock.

First you have to remove the rear shock.
http://i142.photobucket.com/albums/r87/ ... eload1.jpg

Then find 2 square edged spacers the same thickness. The thickness ideally should be about 1/3rd the full travel of the shocks spring preloader housing as it separates from the minimum preload resting stop. Some judgment will help a lot in recovering 110% of the useful preload travel that was lost. The good news is that you can add too much oil and slowly bleed off a suitable amount at the minimum setting while watching the excessive gap (where the spacers were) diminish. Here's 2 pics to show what I'm talking about:

http://i142.photobucket.com/albums/r87/ ... eload3.jpg
http://i142.photobucket.com/albums/r87/ ... eload2.jpg

Since I overcharged the preload system, I did not crank it to maximum preload and risk overextending the shock's preload piston. I just put it 5 turns inward and kept on test riding & adjusting it higher until neutral cornering fall-in was attained. I now have my SportBike handling back again, even with Ann on the back and the system city cases loaded with stuff. I also have some in reserve for future weepage.

FYI - - - Links were provided, rather than forced image display, to cut down on our bandwith penalties and display times for our Dial-Up buddies.

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[towerworker]

Rob--

Is milage the big factor in shock wear? Or is time (age) a factor as well?

I have an 04 now with 17K on it. Haven't ridden it enough yet to really feel it out.

Wayne

[CycleRob]

Wayne,
It's prolly a little of both. You can ride very little mileage thru all kinds of foul weather or very bumpy back roads and that's not good. Dirty street water or 80,000 bump cycles isn't the flawlessly polished chrome shock shaft's best friend. On the other end, a lot of miles can be mostly a lot of glass smooth freeway miles.

Our buddy WNCBMW has a close friend that replaced the seals and oil in my rear Ohlins shock at a great price. He services many dirtbike shocks out of his basement business and knows all the facts you want to know. I almost remember him saying the shock oil should be changed like every 20K(?) miles.
The oil in my shock was leaking and real dirty with ~22K miles.

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[boxermania]

Darn I just went into great detail on the same topic on another post for snowprick as an adder to his hose interference with the swing arm.

Heck, had I seen this post I would have refered to it......I better start checking all the recent posts before going into long and lengthly repeats.....

[snowprick]

Darn I just went into great detail on the same topic on another post for snowprick as an adder to his hose interference with the swing arm.

Heck, had I seen this post I would have refered to it......I better start checking all the recent posts before going into long and lengthly repeats.....

Thanks boxermania, your effort was appreciated.

[ladybeemer]

Rob,

I tried to search for the article I read a year or so ago about filling the preload thingy; something I feel quite confident I can do!

I believe you were the author? Would you mind sending me the instructions?

TIA
Linda

[Beemeridian]

54

[CycleRob]

I did have something but it's hiding really good. I didn't invent the oil adding technique. I only added in my version of it. Here's a new one:

When new, your bike handled like a SportBike, now it's almost as bad as a chopper, even with the preload at the maximum stop. It's typical for this to happen over 3 or 4 years and it's caused by rear shocks that have lost their original full range of preload adjustment. The hydraulic preload adjuster on your OilHead can cause a problem with the loss of the rear's normal ride height and eventually increase the bike's unwillingness to corner at road speeds. An Ohlins rear shock has an identical preload system and these instructions are perfect for them too. The hydraulic oil in the preload circuit seems to leak away slowly enough to evaporate and/or be washed away without a trace. Refilling it again restores the full range of adjustment to like new. This preload oil supply is completely separate from the shock's suspension oil and at the minimum preload setting it's hydraulic pressure goes to zero. This characteristic allows us to easily, with just 2 wrenches, add hydraulic preload oil to replace any that was lost.

The easiest way to test for oil loss is to loosen the adjuster knob till you feel the heavy resistance go away. That is the point where the hydraulic adjuster ceases to compress the rear spring and it's bottomed out. Note and mark that location on the knob then continue turning the knob CCW counting the turns. If the point of no resistance isn't within 1.5 turns of the top end stop of the adjustment knob's travel, then you have too much lost motion and should add more oil. Turn the adjuster FULLY CCW to the stop and before you remove the adjuster from it's mounting bracket, mark the location on the adjuster body the direction the hose comes out from. This is very important later on so the hose doesn't point toward the muffler or swingarm!! If you have to loosen it again to locate it correctly, you will loose some valuably needed oil.

Now, get a box wrench and slightly loosen the banjo bolt that attaches the hose to the adjuster body. Loosen it to undo it's full torque tightness, tighten it back again just enough so it doesn't leak oil and you will be able to loosen it again by holding the assembly in your hand. Remove any hose clamps and dismount the adjuster assembly. While holding the adjuster upside down with the banjo bolt on top, remove the banjo bolt fitting at the adjuster and keep the hose end vertical so no oil seeps out. When you unthread it, keep the bolt and sealing washer on each side of the fitting all together. So, the banjo bolt travels with the hose end, held high by your creativity. Be sure the adjuster is fully counter clockwise to it's stop and stick a clean, long, small screwdriver, allen wrench or similar thru the oil in the hole where the banjo fitting attaches and push the oil submerged piston all the way down until it stops. It should only move a 1/2" or less, but that is good. There is no spring return to move the internal piston to the minimum stop, the big shock spring does that, so you have to push it there manually. Keep the adjuster upside down during this entire process. You should now see the oil level has gone down inside the threaded hole. You had a problem and adding oil will fix it.

Next you add power steering fluid, ATF or engine oil (doesn't matter much) into the adjuster's banjo bolt hole until it's level with the top. Re-install the banjo fitting with the washers, locate it where you marked it and tighten the bolt. remount the adjuster to the bike then fully tighten the line's banjo bolt. Now check the adjustment range. From the minimum setting you'll get spring compressing hydraulic resistance right away.

Problem solved.


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[ladybeemer]

Rob,

Thanks for the post....I have a printed copy now! I'll have a go at this in the next few weeks.

Rode about 260 miles yesterday and best of all.....my wheel stayed on.

[Beemeridian]

77

[Beemeridian]

33

[CycleRob]

There is another problem with our bikes handling that happens when you do too much 70mph super slab and the tires get squared off. When they get worn out mostly in that manner and are nearing the tire's last remaining legal tread life, the handling gets "reluctant", even with the max preload dialed on. That's annoying.

That's where my bike is now. Today I backed off the Ohlins preload adjuster from max preload just to see if I still had the full travel. It did. All 25 turns were doing work. Tire pressures were 38F, 42R. I was suspicious because the handling required what I feel is considerable countersteer to initiate and maintain a corner.

I'll be combining a Pilot Road-2 tire set replacement with my 770 mile trip to the May Bash, but plans so far make it AFTER the event at my shop in Washington NJ. I might need a new plan.


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[bikermeow]

For extra "flickability", I suggest changing the rear strut to that of a R1150GS, shortens the wheelbase and enhances ease of turning.

Cheers

Cat